1. Field of the Invention
This invention relates to medical devices, and more particularly, to prediction and detection of physiological events.
2. Background
Many diagnostic and therapeutic medical devices are equipped to detect physiological events. For example, a widely respected diagnostic test for sleep-related disorders, such as obstructive sleep apnea syndrome, is polysomnography, in which respiratory, cardiac, muscular, and neurological parameters are monitored during sleep by a polysomnogram.
The polysomnogram will typically record data from a number of different data sources requiring a number of wire attachments to the patient—often more than 20 different wires are used. These data sources typically include:                one or more electroencephalogram (EEG) channels to monitor brain activity,        one or more pressure transducers, thermocouples, and/or thermistors, fitted in or near the nostrils, for monitoring nasal airflow and/or temperature,        one or more microphones to monitor breathing sounds, including snoring,        one or more electromyogram (EMG) channels for measuring chin and/or leg movements,        one or more electrooculogram (EOG) channels to monitor eye movements,        one or more electrocardiogram (EKG) channels for detecting heart rate and rhythm, including heart rate variability (HRV),        a pulse oximeter to measure oxygen saturation of arterial hemoglobin, and/or        belts placed around the patient to measure chest wall and abdominal wall movement.        
In conjunction with assessment of daytime symptoms, using a polysomnogram to measure the frequency of sleep-related apnea (cessation of breathing) and/or hypopnea (marked reduction in tidal volume) represents the standard of care for diagnosing obstructive sleep apnea (OSA) syndrome.
Obstructive sleep apnea syndrome is the most common sleep-related breathing disorder, with a prevalence of at least 4% in men and 2% in women aged 20 to 60 years, and thus is a major public health problem with a societal impact comparable to that of smoking Studies have revealed associations with cardiovascular disease, stroke, and diabetes and people with obstructive sleep apnea syndrome commonly experience excessive daytime sleepiness and cognitive dysfunction, placing them at risk for motor vehicle accidents and work related injuries.
The most common therapy for obstructive sleep apnea syndrome is continuous positive airway pressure (CPAP), which attempts to overcome mechanical collapsing forces in the airways by continuously blowing air into the nose. Although largely effective, for many CPAP is cumbersome and difficult to tolerate, resulting in poor long-term compliance. To reduce pressure exposure, auto-adjusting positive airway pressure (APAP) devices are used in some cases. APAP devices typically rely on early detection of respiratory events to make pressure adjustments.
These conventional therapies for obstructive sleep apnea syndrome are largely effective but suffer from poor patient compliance. In some patients, the conventional therapies do not fully alleviate all adverse consequences, including obstructive-sleep-apnea-associated cardiovascular risk factors, daytime sleepiness, and decreased quality of life. Methods and devices capable of detecting and predicting individual physiological events, such as apneas and hypopneas, are needed to provide improved treatment, compliance, and effectiveness of these conventional therapies.